HIV-1 disease is a serious international health problem and a major cause of death in sub-Saharan Africa. Therapeutic and preventative treatments are limited in availability and effectiveness, thus critical evaluations of alternative approaches to control this virus are greatly needed. The overall goal of this project is to elucidate the mechanisms underlying naturally occurring protective immunity to HIV-1 disease in sub- Saharan Africa. The specific aims are (1) to determine the role of NK-cells in decreasing mother to child HIV- 1 transmission and in slowing HIV-1-disease progression to AIDS in adults and (2) to determine the molecular mechanisms of HLA-Bw4 80! mediated protection from HIV transmission and disease progression. In the first aim we will conduct a cross-sectional study by collecting peripheral blood samples from mothers who are HIV-transmitters versus non-transmitters and assessing their NK-cell responses to HIV-infected self and child-derived T cells by the production of anti-viral soluble factors (e.g., interferon-y, MIP-1a &(3, and RANTES) as well as by cell-killing assays. We will also conduct a similar analysis with blood samples from HIV-1-infected adults that are virus controllers compared to virus non-controllers. To address the second aim we will generate reporter cells expressing NFAT-LacZ and the NK cell receptor, KIR3DS1. We will assess HLA-B recognition by KIR3DS1 by in vitro co-culture assays with HIV-1 infected and uninfected target cell lines expressing the putative ligand, HLA-B57. To probe molecular mechanisms of recognition by KIR3DS1 further, HLA mutagenesis or HIV peptide screening will be employed. The research plan is ideal for the career objective of the candidate, William Carr, to become an independent investigator in international health research, specializing in innate viral immunity. The proposed career development plan will consist of closely mentored basic-science research with Drs. Marcus Altfeld and Bruce Walker as mentors in the U.S. and Drs. Hoosen Coovardia and Salim Abdool Karim as a mentors in South Africa, state-of-the-art research facilities at the Doris Duke Research Center in Durban, South Africa, and at the Partners AIDS Research Center at Massachusetts General Hospital in the U.S., and a didactic curriculum on ethics in international research. This plan is well suited for Dr. Carr to establish long-term scientific collaborations in South Africa and to establish himself as an independent investigator in international health research